Charging devices, in particular exhaust gas turbochargers, are well known from the prior art. In this case, a turbine wheel is driven by a driving fluid, in particular by the exhaust gas, and transmits said driving power via a shaft to a compressor wheel. In order, in particular at different operating points, to increase the power of the charging device, it is furthermore known to provide the charging device with a variable turbine geometry which surrounds the turbine wheel with a plurality of guide blades. It is possible here by means of the guide blades to influence the flow of the driving fluid, that is to say in particular the exhaust gas, to the turbine wheel. For example, it is possible here, in a closed state of the guide blades, to reduce a flow cross section for the driving fluid or exhaust gas such that the driving fluid impinges on the turbine wheel at an increased velocity and drives said turbine wheel more rapidly. The guide blades are customarily mounted rotatably in a blade mounting ring. A cover disc is customarily arranged on that side of the guide blades which faces away from the blade mounting ring. A gap remains here between the guide blades and the cover disc, the size of which gap has to be kept as small as possible to improve the efficiency of the variable turbine geometry.
For this purpose, it is proposed in EP 0 226 444 B1 to insert spacers between the blade mounting ring and the cover disc, said spacers providing a fixed spacing between the cover disc and the blade mounting ring.
In addition, it is proposed in EP 1 577 503 B1 for this purpose to form the cover disc and/or the blade mounting ring in a stepped manner or to provide same with steps.
A disadvantage in the case of variable turbine geometries is in particular the fact that the guide blades are affected by manufacturing tolerances. That is to say, the gap between the respective guide blades and the cover disc varies because of the manufacturing tolerances. As a result, the gap cannot be optimally minimized, in particular because the maximum possible tolerance deviations have to be taken into consideration for the operability of the variable turbine geometry.